/*
 * Copyright 2002-2017 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.web.reactive.result.view.script;

import java.nio.charset.Charset;
import javax.script.Bindings;
import javax.script.ScriptEngine;

import org.springframework.lang.Nullable;

/**
 * An implementation of the Spring WebFlux {@link ScriptTemplateConfig} for
 * creating a {@code ScriptEngine} for use in a web application.
 *
 * <pre class="code">
 * // Add the following to an &#64;Configuration class
 * &#64;Bean
 * public ScriptTemplateConfigurer mustacheConfigurer() {
 *    ScriptTemplateConfigurer configurer = new ScriptTemplateConfigurer();
 *    configurer.setEngineName("nashorn");
 *    configurer.setScripts("mustache.js");
 *    configurer.setRenderObject("Mustache");
 *    configurer.setRenderFunction("render");
 *    return configurer;
 * }
 * </pre>
 *
 * <p><b>NOTE:</b> It is possible to use non thread-safe script engines with
 * templating libraries not designed for concurrency, like Handlebars or React running on
 * Nashorn, by setting the {@link #setSharedEngine sharedEngine} property to {@code false}.
 *
 * @author Sebastien Deleuze
 * @see ScriptTemplateView
 * @since 5.0
 */
public class ScriptTemplateConfigurer implements ScriptTemplateConfig {

    @Nullable
    private ScriptEngine engine;

    @Nullable
    private String engineName;

    @Nullable
    private Boolean sharedEngine;

    @Nullable
    private String[] scripts;

    @Nullable
    private String renderObject;

    @Nullable
    private String renderFunction;

    @Nullable
    private Charset charset;

    @Nullable
    private String resourceLoaderPath;


    /**
     * Default constructor.
     */
    public ScriptTemplateConfigurer() {
    }

    /**
     * Create a new ScriptTemplateConfigurer using the given engine name.
     */
    public ScriptTemplateConfigurer(String engineName) {
        this.engineName = engineName;
    }


    /**
     * Set the {@link ScriptEngine} to use by the view.
     * If {@code renderFunction} is specified, the script engine must implement {@code Invocable}.
     * You must define {@code engine} or {@code engineName}, not both.
     * <p>When the {@code sharedEngine} flag is set to {@code false}, you should not specify
     * the script engine with this setter, but with the {@link #setEngineName(String)}
     * one (since it implies multiple lazy instantiations of the script engine).
     *
     * @see #setEngineName(String)
     */
    public void setEngine(@Nullable ScriptEngine engine) {
        this.engine = engine;
    }

    @Override
    @Nullable
    public ScriptEngine getEngine() {
        return this.engine;
    }

    /**
     * Set the engine name that will be used to instantiate the {@link ScriptEngine}.
     * If {@code renderFunction} is specified, the script engine must implement {@code Invocable}.
     * You must define {@code engine} or {@code engineName}, not both.
     *
     * @see #setEngine(ScriptEngine)
     */
    public void setEngineName(@Nullable String engineName) {
        this.engineName = engineName;
    }

    @Override
    @Nullable
    public String getEngineName() {
        return this.engineName;
    }

    /**
     * When set to {@code false}, a new  {@link ScriptEngine} instance will be created
     * for each request, else the same instance will be reused.
     * This flag should be set to {@code false} for those using non thread-safe script
     * engines with templating libraries not designed for
     * concurrency, like Handlebars or React running on Nashorn for example.
     * <p>When this flag is set to {@code false}, the script engine must be specified using
     * {@link #setEngineName(String)}. Using {@link #setEngine(ScriptEngine)} is not
     * possible because multiple instances of the script engine need to be created for
     * each request.
     *
     * @see <a href="http://docs.oracle.com/javase/8/docs/api/javax/script/ScriptEngineFactory.html#getParameter-java.lang.String-">THREADING ScriptEngine parameter<a/>
     */
    public void setSharedEngine(@Nullable Boolean sharedEngine) {
        this.sharedEngine = sharedEngine;
    }

    @Override
    @Nullable
    public Boolean isSharedEngine() {
        return this.sharedEngine;
    }

    /**
     * Set the scripts to be loaded by the script engine (library or user provided).
     * Since {@code resourceLoaderPath} default value is "classpath:", you can load easily
     * any script available on the classpath.
     * <p>For example, in order to use a JavaScript library available as a WebJars dependency
     * and a custom "render.js" file, you should call
     * {@code configurer.setScripts("/META-INF/resources/webjars/library/version/library.js",
     * "com/myproject/script/render.js");}.
     *
     * @see #setResourceLoaderPath
     * @see <a href="http://www.webjars.org">WebJars</a>
     */
    public void setScripts(@Nullable String... scriptNames) {
        this.scripts = scriptNames;
    }

    @Override
    @Nullable
    public String[] getScripts() {
        return this.scripts;
    }

    /**
     * Set the object where the render function belongs (optional).
     * For example, in order to call {@code Mustache.render()}, {@code renderObject}
     * should be set to {@code "Mustache"} and {@code renderFunction} to {@code "render"}.
     */
    public void setRenderObject(@Nullable String renderObject) {
        this.renderObject = renderObject;
    }

    @Override
    @Nullable
    public String getRenderObject() {
        return this.renderObject;
    }

    /**
     * Set the render function name (optional). If not specified, the script templates
     * will be evaluated with {@link ScriptEngine#eval(String, Bindings)}.
     * <p>This function will be called with the following parameters:
     * <ol>
     * <li>{@code String template}: the template content</li>
     * <li>{@code Map model}: the view model</li>
     * <li>{@code RenderingContext context}: the rendering context</li>
     * </ol>
     *
     * @see RenderingContext
     */
    public void setRenderFunction(@Nullable String renderFunction) {
        this.renderFunction = renderFunction;
    }

    @Override
    @Nullable
    public String getRenderFunction() {
        return this.renderFunction;
    }

    /**
     * Set the charset used to read script and template files.
     * ({@code UTF-8} by default).
     */
    public void setCharset(@Nullable Charset charset) {
        this.charset = charset;
    }

    @Override
    @Nullable
    public Charset getCharset() {
        return this.charset;
    }

    /**
     * Set the resource loader path(s) via a Spring resource location.
     * Accepts multiple locations as a comma-separated list of paths.
     * Standard URLs like "file:" and "classpath:" and pseudo URLs are supported
     * as understood by Spring's {@link org.springframework.core.io.ResourceLoader}.
     * Relative paths are allowed when running in an ApplicationContext.
     * <p>Default is "classpath:".
     */
    public void setResourceLoaderPath(@Nullable String resourceLoaderPath) {
        this.resourceLoaderPath = resourceLoaderPath;
    }

    @Override
    @Nullable
    public String getResourceLoaderPath() {
        return this.resourceLoaderPath;
    }

}
